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Author: James Publish Time: 20-01-2021 Origin: Site
Fiber Optic Cable Selection Guide
OM and OS are fiber optic cable categories used to describe multimode and singlemode cable performance. In practical selection, OM fiber is usually chosen for short-distance LAN and data center links, while OS fiber is used for longer backbone, campus, FTTH and telecom transmission. The correct choice depends on transmission distance, optical module type, bandwidth target, installation environment and future upgrade plan.
Quick Takeaway
● Choose OM3 / OM4 for most short-distance 10G, 40G and 100G multimode links in data centers and equipment rooms.
● Choose OM5 only when the optical system specifically uses SWDM / wideband multimode transmission or when project specifications require OM5.
● Choose OS2 for outdoor, campus, FTTH, telecom and longer-distance links where singlemode optical modules are used.
● Do not treat fiber category alone as a distance guarantee. Final reach depends on transceiver type, link loss budget, connector quantity, splice loss and installation quality.
Fiber optic cables used in structured cabling and telecom networks are commonly divided into two broad groups: multimode fiber and singlemode fiber. Multimode cable categories use the prefix OM, while singlemode cable categories use the prefix OS.
OM fiber has a larger core, usually 50 µm or 62.5 µm, and allows multiple light paths to propagate through the fiber. It is mainly used for short-distance links inside buildings, campuses, equipment rooms and data centers. OS fiber has a much smaller core, typically around 9 µm, and supports a single optical path for lower dispersion and longer transmission distance.
| Category | Fiber Type | Typical Core | Main Use | Light Source | Common Wavelengths |
| OM | Multimode fiber | 50/125 µm or 62.5/125 µm | Short-distance LAN, data center and enterprise links | LED or VCSEL | 850 nm / 1300 nm; OM5 also supports wideband operation in the 850–953 nm window |
| OS | Singlemode fiber | Approx. 9/125 µm | Long-distance backbone, campus, FTTH, ISP and telecom links | Laser diode | 1310 nm / 1550 nm |
OS1 and OS2 singlemode fiber are both used with singlemode optical systems, but their cable construction and attenuation targets are different.
OM1 and OM2 are mainly used in legacy or lower-speed multimode systems.
Technical DifferenceThe main technical difference is the fiber core size and propagation mode. OM multimode fiber supports multiple light paths, which makes connection alignment easier but also creates modal dispersion. OS singlemode fiber supports one main optical path, giving it much better long-distance transmission performance. | Practical DifferenceOM fiber is usually more cost-effective for short links because multimode transceivers can be less expensive. OS fiber is usually selected when the distance is longer, when the network must support telecom-grade transmission, or when future high-speed upgrades may require singlemode infrastructure. |
| Decision Factor | OM Multimode Fiber | OS Singlemode Fiber |
| Best distance range | Short distance, typically inside buildings, equipment rooms and data centers | Medium to long distance, including campus, FTTH, metro and telecom routes |
| Core size | 50/125 µm or 62.5/125 µm | Approx. 9/125 µm |
| Dispersion behavior | Higher modal dispersion, distance is more limited | Lower modal dispersion, better for long-distance transmission |
| Optics cost | Often lower for short-reach links | May be higher depending on transceiver type and reach |
| Typical applications | LAN, data centers, server rooms, short backbone links | FTTH, ISP networks, outdoor backbone, campus links, telecom transmission |
OS1 and OS2 are both singlemode fiber cable categories. The practical difference is not the core size, but cable construction, attenuation performance and intended installation environment. OS1 is generally associated with indoor tight-buffered cable construction, while OS2 is generally associated with outdoor loose-tube or blown fiber construction and lower attenuation.
Singlemode fiber uses a small core to reduce modal dispersion and support longer optical links.
| Feature | OS1 | OS2 |
| Fiber mode | Singlemode | Singlemode |
| Typical construction | Indoor tight-buffered cable | Outdoor loose-tube, blown fiber or low-water-peak singlemode cable |
| Typical attenuation category | Up to about 1.0 dB/km, depending on standard and wavelength | Up to about 0.4 dB/km, depending on standard and wavelength |
| Typical use | Indoor building backbone and riser cabling | Outdoor, campus, FTTH, telecom and long-distance backbone cabling |
| Selection note | Choose when the project is indoor and the specification requires OS1 | Choose for most new outdoor or long-distance singlemode projects |
Engineering note: Do not write “OS2 = 80 km” as a fixed rule. OS2 cable can support long-distance applications, but the real distance is determined by transceiver reach, power budget, connector count, splice loss, cable attenuation and safety margin.
Multimode fiber is widely used for short-distance optical transmission. It has a larger core than singlemode fiber, allowing multiple light modes to travel through the fiber. The higher the OM grade, the better the bandwidth and high-speed transmission capability, especially for laser-optimized OM3, OM4 and OM5 systems.
Multimode fiber is commonly used for short-distance LAN, enterprise and data center connections.
OM3 and OM4 are laser-optimized multimode fibers widely used in 10G, 40G and 100G data center cabling.
OM5 is wideband multimode fiber designed for short-wavelength division multiplexing applications.
| MMF Type | Core / Cladding | Typical Jacket Color | Optical Source | Design Focus | Typical Application |
| OM1 | 62.5/125 µm | Orange | LED | Legacy multimode fiber, lower bandwidth | Legacy LAN, low-speed short-distance links |
| OM2 | 50/125 µm | Orange | LED or older multimode optics | Higher bandwidth than OM1, but not optimized for modern high-speed data centers | Legacy enterprise and short-distance 1G links |
| OM3 | 50/125 µm | Aqua | VCSEL | Laser-optimized multimode fiber | 10G links up to 300 m; 40G/100G short-reach data center links depending on optics |
| OM4 | 50/125 µm | Aqua or violet | VCSEL | Higher effective modal bandwidth than OM3 | Longer 10G multimode links and 40G/100G data center links |
| OM5 | 50/125 µm | Lime green | VCSEL / SWDM optics | Wideband multimode fiber for short-wavelength division multiplexing | SWDM systems and projects requiring OM5 compatibility |
The table below is a practical planning reference. Always check the optical transceiver datasheet, standards requirement and link loss budget before final project approval.
| MMF Category | 1000BASE-SX | 10GBASE-SR | 40GBASE-SR4 | 100G Short-Reach Notes | Selection Comment |
| OM1 | Up to 275 m | Up to 33 m | Not recommended | Not recommended | Use mainly for legacy systems |
| OM2 | Up to 550 m | Up to 82 m | Not recommended | Not recommended | Use for legacy or low-speed short links |
| OM3 | Project-dependent | Up to 300 m | Up to 100 m | Commonly 70–100 m depending on optic type | Good baseline for many data center links |
| OM4 | Project-dependent | Up to 400 m under 10GBASE-SR planning | Up to 150 m | Commonly 100–150 m depending on optic type | Preferred for higher margin and longer multimode reach |
| OM5 | Project-dependent | Similar planning class to OM4 for many non-SWDM systems | Up to 150 m | Can support SWDM or wideband applications when optics are compatible | Choose when SWDM or project specification requires OM5 |
Pass: Recommended Choices● Use OS2 for new outdoor, FTTH, campus and long-distance singlemode links. ● Use OM4 when a data center needs more multimode distance margin than OM3. ● Use OM3 for cost-sensitive 10G or short 40G / 100G multimode links. | Warning: Check Before Ordering● Do not mix OM1 / OM2 with OM3 / OM4 without checking the optical channel design. ● Do not choose OM5 unless the optic or project specification benefits from wideband multimode fiber. ● Do not rely only on jacket color; confirm printed cable marking and datasheet values. |
| Project Situation | Recommended Fiber | Reason |
| FTTH drop, telecom access, outdoor backbone | OS2 singlemode | Better for long-distance links and low attenuation requirements |
| Indoor building backbone with singlemode optics | OS1 or OS2 | Follow project specification; OS2 is often preferred for performance margin |
| 10G data center link under 300 m | OM3 | Common cost-effective choice for 10GBASE-SR links |
| 10G data center link requiring more distance margin | OM4 | Higher bandwidth and longer 10G multimode reach than OM3 |
| 40G / 100G parallel multimode cabling | OM3 or OM4 | OM4 usually provides more distance margin for SR4 applications |
| SWDM or wideband multimode application | OM5 | Designed for wideband multimode transmission across multiple short wavelengths |
ZION can supply singlemode and multimode patch cords in SC, LC, FC, ST and MPO/MTP connector formats. The examples below are organized by fiber type to help buyers connect the article content with practical product selection.
| Fiber Type | Image | Product | Recommended Use | Key Notes |
| OS2 Singlemode |  | SC/APC-SC/APC Singlemode Patch Cord | FTTH, ODN, telecom access and long-distance singlemode links | 0.9 / 2.0 / 3.0 mm cable options, PVC or LSZH jacket, APC polish available |
| OS2 Singlemode |  | LC/UPC-LC/UPC Singlemode Patch Cord | High-density singlemode patching in racks, ODF and equipment rooms | Suitable for G.652.D / G.657.A1 / G.657.A2 configurations depending on project request |
| OS2 Singlemode |  | FC-FC Singlemode Patch Cord | Telecom, testing and applications requiring threaded connector stability | Zirconia ceramic ferrule, PC / UPC / APC polish options |
| OM1 / OM2 Multimode |  | LC-ST Multimode Patch Cord | Legacy multimode LAN, enterprise networks and short-distance links | OM1 62.5/125 µm or OM2 50/125 µm available by project requirement |
| OM3 Multimode |  | LC/UPC-LC/UPC OM3 Patch Cord | 10G data center and short-distance high-speed multimode links | 50/125 µm laser-optimized multimode fiber, aqua jacket |
| OM3 Multimode |  | MPO-MPO OM3 Patch Cord | 40G / 100G parallel optical cabling in data centers | 12 / 24 fiber cores, LSZH jacket, high-density cabling |
| OM4 Multimode | | LC/UPC-LC/UPC OM4 Patch Cord | Higher-speed multimode links requiring more distance margin | 50/125 µm, higher modal bandwidth than OM3 |
| OM4 Multimode |  | MPO-MPO OM4 Patch Cord | 40G / 100G data center cabling with higher reach margin | 12 / 24 fiber cores, LSZH jacket, MPO polarity options |
Product note: Patch cord pages may be organized by connector type, cable diameter and jacket material. For exact OM / OS grade, confirm the printed cable marking, datasheet, core size, jacket color, insertion loss grade and required test report before ordering.
For new long-distance or outdoor singlemode projects, OS2 is usually preferred because of its lower attenuation. However, if the project specification calls for OS1 in an indoor environment, OS1 can still be suitable.
They can often be physically connected because both are 50/125 µm multimode fibers, but the channel performance will be limited by the lower-grade fiber and total link budget.
No. Many 100G multimode links use OM3 or OM4 depending on distance and optic type. OM5 is mainly useful when the system uses SWDM or when the project specification requires wideband multimode fiber.
FTTH networks normally use singlemode fiber, commonly OS2 or bend-insensitive singlemode fibers such as G.657.A1 / G.657.A2 depending on drop cable routing and bend requirements.
Share your required data rate, link distance, connector type, installation environment and optical module model. ZION can help confirm the suitable fiber type, cable structure, jacket material, connector polish and test requirement.
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